Mechanical Energy Aided Aluminizing Mechanism And Characterization Of Structure And Properties Of Aluminized Layer

The effects of agent formulation, temperature, time, speed of the cylinder, proportion of the permeability agent, diameter of the cylinder, particles size of permeability agent, impact particles on the mechanical aided aluminized speed are studied. The metallographic analysis, microhardness tester, electron probe and TEM are used to investigate the structure, morphology and chemical composition distribution of the aluminized layer, and the influence of mechanical energy on the microscopic flaw of the sample substrate are studied.By using the chemical reaction thermodynamic functions, the process and steps of mechanical energy aided chemical reaction are analyzed. The thermodynamics and kinetics mechanism of infiltration agent reaction, the adsorption and diffusion of active atomic in the mechanical energy aided aluminized process are studied. So we can ascertain the control step and the non-control step of the aided process. On this basis, a mechanical energy aided aluminized theoretical model is established.We test the microhardness, corrosion resistance, high temperature oxidation resistance, and the influences of the aluminized layer on the substrate tensile strength, elongation and other mechanical properties. Then we obtain the follow conclusions:1. Choosing suitable aluminum provider, catalytic agent and stuffing, uniform and compact alumimzed layer with the thickness more than 250μrn would be obtained at the low temperature of 500-650℃. By this method, the aluminized speed could reach the speed of the high temperature powder aluminizing (above 900℃). Loosen structure is apt to be formed in the layer.2. The higher the aluminized temperature, the faster the aluminized speed. If the stuffing particles are small, the Al powder will dissolve when the aluminized temperature is higher than 650℃, because the fluid of the permeability agent is poor, the thickness of aluminized layer will decrease. So the temperature of mechanical energy aided aluminizing should be controlled between 500℃and 650℃. If the stuffing particles is coarser, the fluid of permeability agent will be finer, mechanical energy aided aluminized speed is fast at 700℃, 08F steel with the aluminized thickness 250μm can be obtained. However, Al powder of permeability agent bonds into big balls, so it is caused waste. The thickness of aluminized layer related to holding time is in a parabola form. The aluminized speed is the fastest when the rotational speed of cylinder is 8r/min and the performed gap of cylinder is 10%.3. The internal organization of aluminized layer is mainly composed phase, which grow in columnar form into the substrate. A little of FeAl, compound and amorphous alloy phase are formed in alumimzed layer. The low Al phase region of FeAl, Fe₃Al are not formed between Fe₂Al₅ and substrate, the transition phase ofα-Fe containing Al do not form coarse grain size.4. The gains of Al₂O₃, Fe₂O₃ and FeO·Al₂O₃ oxide are discontinuously distributed on the surface of Fe₂Al₅ phase in the surface texture of aluminized layer. The oxides is formed earlier than Fe₂Al₅ phase.5. The thickness of aluminized layer decreases along with the increase of carbon content. By mechanical energy aided aluminizing, the aluminized layer can be also obtained on the surface of 1Cr18Ni9 stainless steel, Ti and Ni, but the permeability speed is much slower than low carbon steel. The aluminized layer can not be obtained on the Cu surface by mechanical energy aided aluminizing. The aluminized layer obtained on Mg surface is crisp and easily flaking.6. At the temperature of 500℃to 700℃, the powder aluminized process is a thermodynamic spontaneous process. The agents produced active atomic is the control step during the process of reaction, adsorption and diffusion.7. Mechanical energy aided alumimzed mechanism is mainly because of agents vibration and friction, which can enhance internal defect density and the surface activity of the permeability agents, increase the contact chance of different component of agents, permeability agents and samples surface, so the aluminized reaction is accelerated, the concentration of active aluminum atoms is increased remarkably. The relative shift between agents and samples and mutual friction make the surface oxide film of samples become discontinuous, so the samples surface are purified, which would be benefit to adsorb active atom and enhance the aluminized speed too. 8. HCl generated from catalystic agent NH₄Cl can not remove all the FeO film on the surface of samples. The active Al atoms come into Fe₂O₃ film firstly, and grab the oxygen atoms and generate Al₂O₃, the Fe element is deacidized, but Fe and Al atoms do not combine into Fe-Al compounds, Fe is existed in the form of FeO. The oxide particles of (FeO)_n(Al₂O₃)_m are formed on the surface of aluminized layer.9. The microhardness of aluminized layer reach 980HV_0.1 by mechanical energy aided aluminizing. Mechanical aided aluminized layer has excellent corrosion resistance to NaCl, H₂S, H₂SO₃, HNO₃ and high temperature oxidation resistance. The substrate could maintain high mechanical properties after mechanical energy aided aluminizing, and this method could be applied to the workpieces with complex shapes, so the mechanical energy aided process has a good prospect.